Rescue services, giving an early toll, said 30 people had been hospitalised, and eyewitnesses said they had seen others fall or jump from the stricken building.

Flames ravaged the tower, lighting up the pre-dawn west London skyline and sending up a thick plume of black smoke.

Large pieces of debris could be seen falling from Grenfell Tower, a 1970s block in the working-class north Kensington area — a short distance from chic Notting Hill.

Witnesses said they heard screaming from the upper floors as the flames rose in the night and one desperate resident could be seen waving a white cloth from a top floor window.

“They were trapped. They couldn’t come downstairs, especially from the top floor … people have been burned,” a witness identified as Daniel told BBC Radio London.

“I have seen it with my own eyes. And I have seen people jump.”

Another witness named as Jody Martin told the BBC that he battled his way his way to the second floor only to encounter choking smoke.

“I watched one person falling out, I watched another woman holding her baby out the window… hearing screams, I was yelling everyone to get down and they were saying ‘We can’t leave our apartments, the smoke is too bad on the corridors’,” he said.

By early morning, most of the block was a blackened hulk. Clouds of smoke rose into the sky as firefighters sprayed water onto floors within reach of appliances on the ground.

Frantic families at the scene attempted to call their loved ones, fearing they could be stuck inside, and were being directed by police to a nearby restaurant where some of the injured were being treated.

The fire brigade said 40 fire engines and 200 firefighters had been called to the blaze at Grenfell Tower, which has 120 flats.

“Fire is from second to top floor of 27 storey building,” the fire service said on Twitter. Firefighters had managed to evacuate residents up to the 11th floor.

“We can confirm that we have taken 30 patients to five London hospitals following the incident,” said Stuart Crichton, assistant director of operations at the London Ambulance Service.

He added that more than 20 ambulance crews as well as a “hazardous area response team” were at the scene.

“Our priority is to assess the level and nature of injures and ensure those in the most need are treated first and taken to hospital.”

Police cleared nearby buildings because of fears about falling debris and shut down a section of the A40 highway — a normally busy thoroughfare into London.

A London Underground line passing the area near Latimer Road station was also shut down.